This invention relates to a sealing ring having at least one surface serving as a sliding face being in a face-to-face sliding engagement with a counter-face. Such a sealing ring comprises a low-friction material and is preferably a compressed, metal fiber body of superior high temperature-resistant properties. The sealing ring may find advantageous use, for example, in articulated exhaust pipes for internal combustion engines. The sliding faces of the sealing ring may be coated with a low-friction material.
To neutralize vibrations caused by an internal combustion engine it is known to make the ends of the exhaust pipe and the exhaust manifold generally as ball joint elements having a spherical half and a complemental, dished half and to urge these components axially together by a resilient clamping arrangement. Such a connection permits a certain relative angular displacement of the interconnected tubular parts. The required sealing ring interposed between the ball and the socket of the ball joint is adapted to the contour thereof and thus has a sliding face shaped as a spherical segment. In such a construction the sealing ring also serves as a slide bearing for the interconnected pipe ends.
As noted earlier, such sealing rings are made of low-friction materials. Preferably sealing rings of compressed metal fibers and low friction substances are used. For example, according to German Offenlegungsschrift (Non-examined Published Patent Application) No. 2,829,333, a steel mesh which is coated with a low-friction material such as graphite or mica scales or flakes, is spirally wound to form a ring blank which is subsequently pressed to the desired shape. According to German Pat. No. 2,845,949 a ring skeleton made of long steel fibers is pre-pressed, the obtained body is penetrated and coated with a low-friction material such as graphite powders or mica powders and thereafter the body is pressed to the desired final shape. In such rings the long fibers, however, can pierce the outer, low-friction layers and thus the latter may break off or peel off, whereupon the exposed fibers directly contact the pipe end and cause noise, worn traces with subsequent corrosion phenomena.
To avoid the above-outlined occurrences and to thus minimize wear phenomena, German Pat. No. 3,107,920 discloses the use of a metal fiber wool with a random alignment of the metal fibers for making the ring skeleton. The metal fibers have short lengths which, apart from their simpler manufacture, reduce wear and corrosion phenomena.
While in practice, such rings avoid the wear and corrosion phenomena to a great extent, nevertheless, during engine operation, between the joined exhaust pipes relative motions occur which, despite the high proportion of friction reducing material and occasionally graphite layers, disadvantageously result in noise emission, particularly in the generation of squeaking noises.
To avoid such occurrences, according to German Pat. No. 3,234,376, to the short-fiber low-friction mixtures inorganic or organic substances are mixed which, at elevated temperatures, react with the metal fibers heated by friction and smoothen the sliding faces of the rings. While in this manner noise generation is reduced during normal operation, such noises could not be entirely eliminated, particularly in the break-in phase of the rings because of the only slowly developing polish.
It is further known to provide the sliding faces of the rings with thin coatings, particularly of polytetrafluoroethylene, to eliminate noise generation. Such coatings, however, begin to flow plastically on the sliding face in response to pressure, temperature and friction stresses and are relatively rapidly destroyed during the break-in period of the engine. A permanent elimination of noise generation at the seal is therefore not feasible with such measures.